TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Charging S70D and Solar Array

Discussion in 'Model S: Battery & Charging' started by Vistan, Mar 14, 2016.

  1. Vistan

    Vistan Member

    Joined:
    Dec 21, 2015
    Messages:
    12
    Location:
    Vista, CA
    I am both a new S70D owner and a new poster. I've searched here for info on this issue, but no luck.

    I live in North San Diego County and am at the mercies of San Diego Gas & Electric. About a year ago, I installed a solar array on my roof which was sized to cover my electrical use history. It is a 3.9kw array , which over the past year averaged 577kwh per month with a variation of 420kwh in the winter to 700kwh in the summer months. With the exception of two hot months last fall, when I was forced to run air conditioning, the array has nicely covered all our needs, and allowed us to send power back to the grid. I bought the car at the end of December, and am wondering how best to charge it (I do have a 240v/50a circuit). We don't drive it all that much, maybe about 15-20 miles per day on average, which includes several trips to Palm Desert where I can use a Supercharger. Questions:

    a. Should I plug it in after every use, even if it's only a few miles? Our current mode is to charge every 3 days or so. i.e., frequent small charges vs. periodic larger charges?

    b. Is it better to charge when the sun is charging the solar array, or at night and taking power from the grid?
    Or, does it not matter? We do not have time of use rates, currently. My grid rate is about 17.5 cents/kwh.

    c. Is it cost effective to increase the capacity of the solar array to cover the car needs. This is feasible, but I suspect not worthwhile.

    d. Is more info needed?
     
  2. CHG-ON

    CHG-ON Still in love after all these miles

    Joined:
    Jun 24, 2014
    Messages:
    2,754
    Location:
    Santa Cruz Mountains, USA
    Tesla recommends that we always leave the car plugged in. I think the issue of day vs. night depends of what you make from the utility in payback. The car uses minimal energy after charged up to your set point and only maintaining the car. Others may argue with this point. But the cost is negligible, IMO. It won't make a difference to the car. 17.5 sounds high to me. So day might be better. But I am not a solar user, unfortunately. So I can only comment from the sidelines on that.
     
  3. AndreSF

    AndreSF Member

    Joined:
    Feb 21, 2016
    Messages:
    183
    Location:
    San Francisco, CA
    The EV rates for San Diego gas and electric look pretty high (up to 46 cents during peak and 18 cents at night), so if your solar systems produces enough kw to cover your car use, I would stick with existing plan (is it a tiered plan?).
    If rate is the same day or night, I would charge at night (every night) just to help with grid load during peak times. You still be using kw produced by your system.
     
  4. Vistan

    Vistan Member

    Joined:
    Dec 21, 2015
    Messages:
    12
    Location:
    Vista, CA
    My existing SDGE plan (which I intend to keep) is tiered at 17 cents/kwh up to 303kwh, then 19 cents/kwh up to 394kwh, then 38 cents/kwh on up. Over the first 15 days of March, my array generated 278kwh, despite several rainy/cloudy days (unusual for San Diego). SDGE pays me about 17.5 cents/kwh that I supply net to the grid.
     
  5. AndreSF

    AndreSF Member

    Joined:
    Feb 21, 2016
    Messages:
    183
    Location:
    San Francisco, CA
    Yeah, that is what I thought. Your existing tiered plan has better peak rates and you generate enough k watts to cover most of your use. Not sure adding more panels would make a lot of sense, like you said, unless you start driving a lot more daily. IMO the idea is to come to net zero, but there will always be some kind of grid fee anyway (PG&E charges $10/mo). I would just charge nightly though.
     
  6. Vistan

    Vistan Member

    Joined:
    Dec 21, 2015
    Messages:
    12
    Location:
    Vista, CA
    AndreSF: Thanks for your input...
     
  7. EMP40

    EMP40 Member

    Joined:
    Mar 8, 2015
    Messages:
    101
    Location:
    Roseville, CA
    Our utility here in Roseville does net metering over the year based on kWh generated vs. used. For us it will make no difference when we charge. We have an an 8.83 kWh Sunpower system, now we just need the Tesla. It depends on how your utility treats any surplus generation during the day.
     
  8. brucet999

    brucet999 Active Member

    Joined:
    Mar 12, 2015
    Messages:
    1,300
    Location:
    Huntington Beach, CA

    By what you write here, it appears that your Tesla uses about 2100 kWh per year (at 300 Wh/mi), so your SDG&E consumption (assuming 15% AC to DC conversion loss) would likely be about 2400 kWh/yr. At 17.5 cents per kWh, your present cost of driving = ca $420 per year.

    Since your solar array pretty much offsets your household usage, then you should be able to balance the annual power cost vs amortized cost (over the projected life of the car less 30% Federal tax credit) of increasing the solar array.
     
  9. smilepak

    smilepak Member

    Joined:
    May 11, 2015
    Messages:
    705
    Location:
    Eastvale, CA
    We have Southern California Edison with Solar Array by Sun Power. For the most part the solar array covers 95% - 105% of our electrical daily use (assuming it is full sun) - minus the cost to charge the S70D. I do set the Tesla to charge after 10:00 PM because it is cheaper to charge after 10 PM. We are on a time of use plan where it is a Peak, Off Peak, and Super Off Peak rate. The Super Off Peak rate for us is approx 11.5 cent starting from 10PM - 7AM. That is when I usually charge the Tesla.

    I drive approx 80 miles per day average. So far my electrical cost per month have been approx $20.00 - $35.00 a month. Most of that is mainly charging the Tesla.
     
  10. ssq

    ssq Member

    Joined:
    Oct 23, 2013
    Messages:
    688
    Location:
    California
    I am glad I found this thread. I am also in SDGE territory and went solar with a 4.7kW system. My household usage is approx 6000 kWh/year. That leaves me with about 2500 kwH/year to spare to charge the X70D when I have it later this year.
    My estimate of EV requirement is :- 12000 miles/year x .45 kwh/mile= 5400 kwh. 5400 - 2000 kwh/year spare production from 4.7 kw system= 3400 kwh/year. Lets assume 4000 kwh/year to factor in more miles driven and charging losses.
    Cost at lowest tier on SDGE is 4000*.017 c/kwh = $680/year. Adding one panel will cost ~$1k ($700 after rebates) and add about 600 kwh/year to capacity.
    I am also on SDGE and I am wondering if going TOU and shifting most usage to the night (washer, dryer, dishwasher, car charging) can further improve the equation for me - I have heard that the ratio of peak costs:eek:ff-peak is as much as 3:1 and production is peak hours with minimal usage can attribute almost a 2-3X multiplier to my spare kwh/year (which is 2000 kwh/year). Or should I add couple more panels (I am on NEM1 and there is very limited time before NEM 1 is gone) to make sure household+EV usage is completely offset. Thanks in advance, my apologies if I am hijacking this thread.
     
  11. gavine

    gavine Petrol Head turned EV Enthusiast

    Joined:
    Apr 1, 2014
    Messages:
    1,007
    Location:
    Southern New Jersey
    Increase your solar capacity if for no other reason than to be green. Driving on sunshine is the future and a great thing. Now that you have more usage and are allowed to increase, why not do it?
     
  12. ssq

    ssq Member

    Joined:
    Oct 23, 2013
    Messages:
    688
    Location:
    California
    For financial reasons :) I like to hit the sweet spot on usage vs. cost, hence the question to help me understand the TOU equation better and/or share TOU experience/data.
    Yes, I could install the largest solar array as an option, but I don't have that kind of free cash flow yet :)
     
  13. gavine

    gavine Petrol Head turned EV Enthusiast

    Joined:
    Apr 1, 2014
    Messages:
    1,007
    Location:
    Southern New Jersey
    Oh. I assumed you had a solar PPA.
     
  14. AndreSF

    AndreSF Member

    Joined:
    Feb 21, 2016
    Messages:
    183
    Location:
    San Francisco, CA
    #14 AndreSF, Mar 24, 2016
    Last edited: Mar 24, 2016
    One of my co-workers has a very similarly sized solar system and drives Leaf. He did switch to PG&E EV-A rate, which essentially TOU you are referring to. His main concern was not with shifting usage that can be shifted, but with something that can't, which is basically running A/C during the day on the hot summer days. However, no issues in the last couple of years at all, and he always came up with more kwh sent to the grid that he needed. Obviously, Leaf has a smaller battery, but this guy drives a lot more that you are planning (about 2oK per year), but does charge at work.
    I would just wait and see when you get your X how things play out before adding any panels, but that is just IMHO :) I don't yet have a solar system, but moving to EV-A plan anyway, as based on what I've seen in the last 3 years I've been charging Volt, my current Model S charging will make up the bulk of our electric consumption, but we do not run A/C.
     
  15. ssq

    ssq Member

    Joined:
    Oct 23, 2013
    Messages:
    688
    Location:
    California
    Good info, thanks! My current system should cover 50% of X needs without TOU, and although I do have the option to charge at work (blink, and a supercharge beside my office) I intend to have full flexibility of charging at home. The urgency behind the question was NEM1 deadline/cap on SDGE. I could potentially add panels to my system and still stay in NEM1 for 20 yrs. If I decide to add panels after NEM1 expiry, I get forced into NEM2 agreements.
     
  16. ssq

    ssq Member

    Joined:
    Oct 23, 2013
    Messages:
    688
    Location:
    California
    I have a paid off 4.7kw (8100 kwh/yr promised production - 9000 kwh/yr actual projected) system. PPA did not make sense to me financially, specially SCTY PPA which increases 2% compounded every yr. I felt buying the system outright was a better choice. Additionally my system is per my design choices of panels, inverter and optimizers which no one was willing to do except few local installers. Oh and I got a kickass pricing - 17k for this 4.7kW system.
     
  17. SageBrush

    SageBrush Active Member

    Joined:
    May 7, 2015
    Messages:
    1,679
    Location:
    Colorado
    Are you asking about money, pollution, something else, or all of the above ?
     
  18. AndreSF

    AndreSF Member

    Joined:
    Feb 21, 2016
    Messages:
    183
    Location:
    San Francisco, CA
    Oh, I see... Well, then adding a panel or two now might not be a bad idea.
     

Share This Page